In a conventional carburetor, a mixing passage through a body of the carburetor mixes and flows a controlled mixture of fuel-and-air into a combustion engine. For controlling the speed of the engine, a rotating throttle valve of a rotary or butterfly type intersects the mixing passage to restrict the volume of fuel-and-air flow to the engine.
A rotary throttle valve is generally a cylinder that seats rotatably and is movable axially, within a cylindrical cavity that intersects the mixing passage. The rotary throttle valve has a through-bore that adjustably aligns with the mixing passage to control flow. A needle of the cylinder projects downward into the through-bore and axially movably into an opposing fuel feed tube of the body to adjustably obstruct an orifice in a wall of the tube that flows liquid fuel into the through-bore. As the rotary throttle valve rotates toward an open position, the through-bore aligns to the mixing passage to increase flow, and simultaneously, the cylinder lifts axially to partially retract the needle from the tube exposing more of the orifice to the through-bore and thus increasing fuel flow.
The butterfly-type throttle valve is generally a pivoting plate disposed in and conforming to the contour of the mixing passage. Like the rotary throttle valve, the butterfly throttle valve controls the amount of fuel-and-air mixture flowing to the engine. Unlike the rotary throttle valve, the butterfly valve does not directly control the amount of liquid fuel entering the air stream.
Both the rotary and butterfly throttle valves, however, have a rotating shaft that projects out of the carburetor body. For some engine applications a lever is attached to this shaft and connected to a Bowden wire or other linkage for a user to remotely rotate the throttle valve. For other applications a lever or knob attached to this shaft is manually grasped and rotated to locally actuate the throttle valve. For instance, a leaf blower utilizing a small two stroke engine may only require local actuation of a throttle valve, and a lawn mower application may require remote actuation.
The cost of manufacturing a wide array of differing parts dependent upon whether an otherwise identical carburetor is remotely or locally actuated and the cost of two subsequent carburetor assembly lines is expensive and time consuming. Yet further, in some applications, it would be advantageous to have the ability to both remotely and locally actuate a carburetor throttle valve that positively and reliably sets the pre-specified engine speeds.